Sidewall imaging transfer (SIT) has become widely used in doubling patterning density. For each SIT process, the final patterning is doubled. Performing SIT twice (SIT2 ) will quadruple patterning density.
An SIT process always results in fins in pairs. However, in some cases it is desired to have an odd number of fins (e.g., some standard cells call for 3-fin field effect transistors (FETs)). Thus, in the conventional SIT process the odd number of fins is usually formed by performing a so-call ‘fin cut’ process which involves patterning and removing the undesired or ‘dummy’ fins after forming a sea of fins.
As fin pitch is increasingly scaled, the fin-to-fin space becomes increasingly narrow. Cutting dummy fins without compromising the adjacent device fins becomes extremely difficult, if not impossible.
Therefore, there is a need for forming an odd number of fins without a fin cut process.